Large Hadron Collider

The Large Hadron Collider (LHC) is by far the most powerful particle accelerator built to date. Following an upgrade, the LHC now operates at an energy that is 7 times higher than any previous machine! The LHC is based at the European particle physics laboratory CERN, near Geneva in Switzerland. CERN is the world’s largest laboratory and is dedicated to the pursuit of fundamental science.

The LHC allows scientists to reproduce the conditions that existed within a billionth of a second after the Big Bang by colliding beams of high-energy protons or ions at colossal speeds, close to the speed of light. This was the moment, around 13.7 billion years ago, when the Universe is believed to have started with an explosion of energy and matter. During these first moments all the particles and forces that shape our Universe came into existence, defining what we now see.

Evolution of the universe after the big bang
(Credit: CERN)

The LHC is exactly what its name suggests - a large collider of hadrons (any particle made up of quarks). Strictly, LHC refers to the collider; a machine that deserves to be labelled ‘large’, it not only weighs more than 38,000 tonnes, but runs for 27km (16.5mi) in a circular tunnel 100 metres beneath the ground. Particles are propelled in two beams going around the LHC to speeds of 11,000 circuits per seconds, guided by massive superconducting magnets! These two beams are then made to cross paths and some of the particles smash head on into one another.

However, the collider is only one of three essential parts of the LHC project. The other two are:

Maintenance on the LHC beamline
(Credit: CERN)

The Detectors
Each of the four main detectors sit in huge chambers around the LHC ring to detect the outcomes of the particles colliding. ATLAS, ALICE, CMS and LHCb.

Worldwide LHC Computing Grid (WLCG)
A global network of computers and software that is essential to processing the masses of data recorded by all of the LHC’s detectors.

The LHC is truly global in scope because the LHC project is supported by an enormous international community of scientists and engineers. Working in multinational teams all over the world, they are building and testing equipment and software, participating in experiments and analysing data. The UK has a major role in the project and has scientists and engineers working on all the main experiments.

In the UK, engineers and scientists at 20 research sites are involved in designing and building equipment and analysing data. UK researchers are involved with all four of the main detectors and the computer GRID. British staff based at CERN has leading roles in managing and running the collider and detectors.

LHC Computing Grid Globe into the computer center
(Credit: CERN)

The total cost of building the LHC was approximately £3.74 billion, made up of three major components1:

The Accelerator (£3 billion)

The Experiments (£728 million)

The Computers (£17 million)

The total cost was shared mainly by CERN's 20 Member States, with significant contributions from the six observer nations.

The LHC project involved 111 nations in designing, building and testing equipment and software, and now continues with them participating in experiments and analysing data. The degree of involvement varies between countries, with some able to contribute more financial and human resource than others.

The LHC has been built in a tunnel originally constructed for a previous collider, LEP (Large Electron Positron collider). This was the most economical solution to building both LEP and the LHC. It was cheaper to build an underground tunnel than acquire the equivalent land above ground. Putting the machine underground also greatly reduces the environmental impact of the LHC and associated activities.

The rock surrounding the LHC is a natural shield that reduces the amount of natural radiation that reaches the LHC and this reduces interference with the detectors. Vice versa, the radiation produced when the LHC is running is safely shielded to the surroundings by 50 – 100 metres of rock.

Can the LHC make a new universe?

People sometimes refer to the LHC recreating the Big Bang, but this is misleading. What they actually mean is:

recreating the conditions and energies that existed shortly after the start of the Big Bang, not the moment at which the Big Bang started

recreating conditions on a tiny scale, not on the same scale as the original Big Bang

recreating energies that are continually being produced naturally (by high energy cosmic rays hitting the earth’s atmosphere) but at will and inside sophisticated detectors that track what is happening

CERN has never been involved in research on nuclear power or nuclear weapons, but has done much to increase our understanding of the fundamental structure of the atom.

The title CERN is actually an historical remnant, from the name of the council that was founded to establish a European organisation for world-class physics research. CERN stands for 'Conseil Européen pour la Recherche Nucléaire' (or European Council for Nuclear Research). At the time that CERN was established (1952 – 1954) physics research was exploring the inside of the atom, explaining the word ‘nuclear’ in its title. The Council was dissolved once the new organisation (the European Organization for Nuclear Research) was formed, but the name CERN remained.

Firstly, CERN and the scientists and engineers working there and their research have no interest in weapons research. They are dedicated in trying to understand how the world works, and most definitely not how to destroy it.

Secondly, the high energy particle beams produced at the LHC require a huge machine consuming 120MW of power and holds 91 tonnes of super-cooled liquid helium. The beams themselves have a lot of energy (the equivalent of an entire Eurostar train travelling at top speed) but they can only be maintained in a vacuum. If released into the atmosphere, the beam would immediately interact with atoms in the air and dissipate all their energy in an extremely short distance.

The LHC does produce very high energies, but these energy levels are restricted to tiny volumes inside the detectors. Many high energy particles, from collisions, are produced every second, but the detectors are designed to track and stop all particles (except neutrinos) as capturing all the energy from collisions is essential to identifying what particles have been produced. The vast majority of energy from the collisions is absorbed by the detectors, meaning, very little of the energy from collisions is able to escape.

Collisions with energies far higher than the ones in the experiment are quite common in the universe! Even solar radiation bombarding our atmosphere can produce the same results; the experiments do this in a more controlled manner for scientific study. The main danger from these energy levels is to the LHC machine itself. The beam of particles has the energy of a Eurostar train travelling at full speed and should something happen to destabilise the particle beam there is a real danger that all of that energy will be deflected into the wall of the beam pipe and the magnets of the LHC, causing a great deal of damage.

The LHC has several automatic safety systems in place that monitor all the critical parts of the LHC. Should anything unexpected happen (power or magnet failure for example) the beam is automatically ‘dumped’ by being squirted into a blind tunnel where its energy is safely dissipated. This all happens in milliseconds, meaning that the particles would have navigated just less than 3 circuits before the dump is complete.